assuming the rock falls straight down, we can determine that this rock is under the influence of solely gravity (the rock is in free fall). therefore, the rock will accelerate at 9.8 m/s^2 (acceleration due to gravity). we can utilize this to solve for vf by plugging our known variables into the kinematics equation vf=v0+at. this will lead us to vf=0+9.8(10), or vf=98 m/s^2. this answer, while correct, seems a tad bit unreasonable, so you should mention to your teacher to consider the feasibility of his physics problems.
